1. Field of the Invention
The invention disclosed herein relates to a chemical vapor deposition process synthesized compounds with the general formula, EQU (HSiO.sub.3/2).sub.n,
with n being an even number ranging from 8 to a very large number. More particularly, it relates to the vapor deposition of oligomeric hydrogensilsesquioxanes, henceforth referred to as hydridospherosiloxanes. The hydridospherosiloxanes are used directly in a chemical vapor deposition reactor to generate films of SiO.sub.2 at low temperatures on substrates that cannot withstand high temperatures.
2. Description of the Prior Art
The use of hydridospherosiloxanes directly in a chemical vapor deposition reactor to generate films of SiO.sub.2 at low temperatures on substrates that cannot withstand high temperatures, is dependent for its commercial feasibility on the commercial availability of hydridospherosiloxanes and on the availability of an economical method of synthesizing these compounds.
The state of the art up to ca. 1980 with regard to the synthesis, properties and uses of the compounds of composition (HSiO.sub.3/2).sub.n with n.gtoreq.8, generally known in the art by the common name hydrogensilsesquioxanes and abbreviated to HT.sub.n, has been summarized in the Gmelin Handbook of Inorganic Chemistry-Si, Supplement Volume B1, pg. 249-251; Publisher Springer-Verlag, Berlin-Heidelberg-New York, 1982. A survey of publications dealing with hydridospherosiloxanes covering the period form 1980 to 1990 shows that the state of the art with regard to the synthesis of the hydridospherosiloxanes has not progressed beyond that described in the publication by C. L. Frye and W. T. Collins in J. Am. Chem. Soc. 1970, 92, 5586-5588 and in U.S. Pat. No. 3,615,272; 1972 assigned to Dow Corning Corporation, Midland, Mich., except in the aspects related to post-synthesis separation methodology. However, these publications, which are listed below, reveal a number of potential applications of the hydridospherosiloxanes which clearly establish the utility of the invention disclosed herein. The publication by V. W. Day et al. in J. Am. Chem. Soc. 1985, 107, 8262-8264 reveals that the compound (HSiO.sub.3/2).sub.8 1 can be used as a precursor for the synthesis of the compounds (ClSiO.sub.3/2).sub.n 2 and (H.sub.3 COSiO.sub.3/2).sub.n 3. Compound 3 can be used as a molecular building block for the synthesis of ceramic materials. Compound 2 has been used as a surface modification agent by R. Beer et al. as described in J. Electron Spectroscopy and Related Phenomena 1987, 44, 121-130. Compound 1 and (HSiO.sub.3/2).sub.10 4 have been used as precursors of functionalized spherosilicates, which have the general formula EQU [SiO.sub.2.5 ].sub.n (Si(CH.sub.3).sub.2 Y).sub.n
where n=8 or 10 and Y may be --CH.sub.2 Cl or --CH.dbd.CH.sub.2, by P. A. Agaskar as described in Synth. React. Inorg. Met.-Org. Chem. 1990, 20, 483-493. The use of these functionalized spherosilicates as precursors of the inorganic/organic hybrid materials called organolithic macromolecular materials (OMM's) is described by P. A. Agaskar in J. Am. Chem. Soc. 1989, 111, 6858. The OMM's can be pyrolyzed under N.sub.2 and converted to microporous ceramic materials by differential leaching with HF.
SiO.sub.2 film deposition has been accomplished primarily through chemical vapor deposition using TEOS at temperatures of about 650.degree. through the oxidation of silane which yields poor quality films.